type inference regression in Base._totuple

[simeonschaub]

This infers correctly in 1.6.1, but doesn't anymore in 1.7:

julia> @code_warntype NTuple{3, Int}(rand(Int, 3))
MethodInstance for Tuple{Int64, Int64, Int64}(::Vector{Int64})
  from (::Type{T})(itr) where T<:Tuple in Base at tuple.jl:314
Static Parameters
  T = Tuple{Int64, Int64, Int64}
Arguments
  #self#::Core.Const(Tuple{Int64, Int64, Int64})
  itr::Vector{Int64}
Body::Tuple{Int64, Int64, Any, Vararg{Any}}
1 ─ %1 = Base._totuple($(Expr(:static_parameter, 1)), itr)::Tuple{Int64, Int64, Any, Vararg{Any}}
└──      return %1

#40561 also doesn't seem to fix this. It would be easy enough to work around this with an explicit type annotation, but it would probably be good to figure out which changes in inference caused this.
Discovered in FiniteDifferences.jl's tests.

[simeonschaub]

bisected to c2ec70c

[aviatesk]

The following diff seems to fix this issue, while keeping the cases addressed by the commit. Not too sure this is the right way to go, though.

diff --git a/base/compiler/typelimits.jl b/base/compiler/typelimits.jl
index 2eb2d6f542..87154839db 100644
--- a/base/compiler/typelimits.jl
+++ b/base/compiler/typelimits.jl
@@ -233,10 +233,6 @@ function type_more_complex(@nospecialize(t), @nospecialize(c), sources::SimpleVe
         tP = t.parameters
         if isa(c, Core.TypeofVararg)
             return type_more_complex(t, unwrapva(c), sources, depth, tupledepth, 0)
-        elseif isType(t) # allow taking typeof any source type anywhere as Type{...}, as long as it isn't nesting Type{Type{...}}
-            tt = unwrap_unionall(t.parameters[1])
-            (!isa(tt, DataType) || isType(tt)) && (depth += 1)
-            return !is_derived_type_from_any(tt, sources, depth)
         elseif isa(c, DataType) && t.name === c.name
             cP = c.parameters
             length(cP) < length(tP) && return true
@@ -267,6 +263,10 @@ function type_more_complex(@nospecialize(t), @nospecialize(c), sources::SimpleVe
                 type_more_complex(tPi, cPi, sources, depth + 1, tupledepth, 0) && return true
             end
             return false
+        elseif isType(t) # allow taking typeof any source type anywhere as Type{...}, as long as it isn't nesting Type{Type{...}}
+            tt = unwrap_unionall(t.parameters[1])
+            (!isa(tt, DataType) || isType(tt) || tt === c) && (depth += 1)
+            return !is_derived_type_from_any(tt, sources, depth)
         end
     end
     return true

[aviatesk]

#40987 will fix this.

[vtjnash]

It looks like _totuple needs to be rewritten. The rewrite of convert for Tuple from last year may supply some guidance.